HOG2 algae issue ..or is it?

[atoll]

After my HOG2 matured I did a first harvest of GHA no problem. However since then I have grown nothing but a dark brown slime cyno algae in it. I am using a powerful air pump so plenty of air. I am not really worried as it must be doing a job even if not growing GHA for some reason. Any ideas why I am only growing slime algae in my HOG? The HOG has been set up 3 or 4 months now
Here is a pic of it just before cleaning. BTW thie amount of slime algae grown was in just 5 days after cleaning.
http://i541.photobucket.com/albums/gg378/lesmelling/Aquareef%20300/20150606_114157_zpsehlicdbx.jpg

After a good scrub with a tooth brush under running fresh water from my tap this is it now and about to go back in my sump.
http://i541.photobucket.com/albums/gg378/lesmelling/Aquareef%20300/20150606_114612_zpspcaqzfas.jpg

[SantaMonica]

Is not cyano; is instead dark slime from very high nutrients. Something recently added nutrients to your water.

[atoll]

Been away for a couple of days and i have a few small growths of GHA in my tank but so far non in my HOG2 as yet. I am going to reduce my feeding for a week or so and see how it goes.